SleepTime

SleepTime is a light-weight app that lives on your menu bar, letting you easily set a timer to put your Mac on sleep automatically after a specified time period you choose.
Not only that! With SleepTime, You can also keep your computer awake and prevent sleep for a period of time.

‣ The Sleep Timer
You are sleeping watching a YouTube video and you dont want your computer to stay on until morning.
Set it to sleep automatically after [X] minutes / hours with the Sleep timer.

When 5 minutes are remaining until going into Sleep, SleepTime will show you the time remaining in your menu bar, allowing you to abort the sleep timer, if needed.

‣ SleepTime gives your Mac some caffeine!
You are doing a critical task on your computer, you dont want it to Sleep every now and then because of the default power/energy settings.
Prevent it from sleeping for a period of time you choose, after which your default Sleep preference should be back to normal.